Looking Up: King Cepheus reins in the northern night sky

Peter Becker More Content Now

Friday

Sep 6, 2019 at 9:40 AM

The “King” among the 88 constellations is neither the brightest nor the most well known, but it is visible every clear night in the Northern Hemisphere and doesn’t even need a telescope to appreciate some of the jewels in his celestial crown.

This is Cepheus the King, who in ancient Greek mythology is the husband of Queen Cassiopeia, also recognized among the stars as the famous “W” (or “M”) pattern circling the North Star.

Cepheus was the King of Ethiopia. He and Cassiopeia had a beautiful daughter, Andromeda, remembered as another constellation, on the other side of Her Majesty.

It has been said that Cepheus was one of the famous band of “Argonauts,” who accompanied Jason on his dangerous expedition in quest of the Golden Fleece. Because of the role Cepheus played, he was honored among the stars.

Ancient Chinese astronomers also pictured royalty here, including the stars we know as Cepheus among the “Inner Throne of the Five Emperors.”

The Arabs, however, imagined a pastoral scene in this section of sky, including a shepherd and his dog guarding a flock of sheep.

Imagining this star pattern as a king takes some imagination. It looks more like a house tottering on the peak of its roof on September evenings. At about 9:30 p.m, this week, Cepheus is found at its highest in the northern sky, above the North Star.

There are five principal stars forming the star pattern, four which make a rough square and the fifth placed where it makes a nearly isosceles triangle. This fifth star points not quite true north.

Rather than an imagined “house” we can imagine the pattern as the head of Cepheus, with the triangle being a pointy cap.

On late winter or spring evenings, Cepheus is found at its lowest point in the north, the “house” or “head” pattern being right-side-up. In early September, however, the sky has not appeared to turn this far, until around 10 a.m. (in broad daylight).

One of Cepheus’ amazing stars is listed as Mu Cephei, nicknamed as the Garnet Star. The famed English astronomer William Herschel (1738-1822) described the star as “garnet” for its vivid red color. Visible to unaided eyes unless there is too much moonlight or light pollution, Mu varies between magnitude +3.4 and +5.1 (average, +4.08) within a wide range, from around 860 days to around 4,400 days.

This star is truly massive. Having a radius about 1,000 times that of the Sun, if Mu Cephei were to replace the Sun in our solar system, Mu would engulf Jupiter and all the inner planets. Mu Cephei is 2,840 lights years away. It takes that many years for its light to reach our eyes. Binoculars show the red color clearly.

Another very interesting star is Delta Cephei. Binoculars will reveal it as a beautiful double star. Delta is also a noted variable star, changing regularly from magnitude +3.8 to +4.6, with a period of five days and nine hours. The yellow-hued star is 990 light years from the Sun.

You can easily track its changing brightness in less than a week. It’s easy to find, at the base of a small triangle of stars of similar brightness.

Most importantly, Delta Cephei gives name to an important class of variable stars, the Cepheids. The period of this class of variable star is dependent on the star’s luminosity (how much light it gives out).

We know the distance to Delta Cephei through its “parallax” - closely measuring how the star seems to shift with respect to background stars, as we observe from different places in the Earth’s orbit. With this knowledge, astronomers can tell the distance of remote galaxies and star clusters by locating a Cepheid variable star and recording its brightness as seen at that distance.

The Milky Way Band passes right through Cepheus; on a moonless night too explore this rich, star-studded area with binoculars or a telescope and find numerous star clusters and other “jewels” of King Cepheus’ “crown.”

The U.S. Navy named two ships after Cepheus.

Full Moon is on Sept. 13.

Keep looking up!Peter Becker is Managing Editor at The News Eagle in Hawley, PA. Notes are welcome at news@neagle.com. Please mention in what newspaper or web site you read this column.